Rope guiding device

ABSTRACT

An adjustable two-piece rope guiding device [21, 26], particularly adaptable for use on offshore guyed tower drilling and production structures [11]. On such structures it is necessary to deflect a taut guy rope [14] into a direction that may not be precisely known, or that may vary with time. Such deflection must not damage the rope by excessive static or cyclic straining or by wearing. To minimize problems of clearance within the structure the guiding is performed in two parts: (1) a permanent deflection into a direction that satisfies the foregoing clearance requirements and (2) a variable deflection occurring beyond clearance problems that completes the required total deflection. When guiding the guy ropes [14] of an offshore oil production tower [11] from their vertical orientation at the clamping and jacking (tensioning) devices [20] on the tower to a seafloor anchoring system [15, 16] a first bending member [21] changes the vertical direction of the guy ropes [14] to a selected direction (plane) extending toward such anchoring system [15, 16]. A second bending member [26] rotates the rope in a new direction at the periphery of the offshore structure [11] to accommodate positions of the anchoring system [15, 16] with respect to the plane of the selected direction. The first member is a fixed shoe [21] having a grooved rope contacting surface [23] and a sleeve [24]. The second member [26] includes an outer fixed housing [45] and an inner rotatable housing [46] having a grooved surface [48] for contacting the rope.

TECHNICAL FIELD

The present invention concerns rope guiding devices and, in particular,rope guiding devices which are applicable for guiding ropes used toanchor marine drilling and production structures.

BACKGROUND ART

There are several offshore platform concepts that have been proposed foruse as drilling and producing platforms in deep water. Some of thoseplatform concepts are designed to permit that platform to move inresponse to wave forces. One such design is the guyed tower. In theguying system for a guyed tower, guylines or ropes are run from theplatform to anchor systems on the ocean floor. The guy ropes are securedat the platform deck by cable grips in a rope tensioning device and passaround deflecting devices or fairleads located below the water surface.The guy ropes then travel outwardly at an angle from the vertical to theanchoring system.

In the past both sheave and shoe type rope-deflecting devices have beenproposed for use at the tower-guy rope juncture. Each type, however,must accommodate for misalignments of the tower and the anchor piles inorder to minimize wear and fatigue of the guyed ropes. Swivel typedeflecting devices have been suggested for this purpose. In the casewhere tensioning devices are located within the interior of the towerstructure a deflecting device should be positioned within the interiorof the tower directly below the tensioning device. The use of a swiveltype deflecting device would result in interferences between the ropeand internal structural elements. The problem then is to deflect a tautrope from the interior of the tower into the direction of the anchoringsystems without interference from structural elements of the tower. Thedirection of the anchoring systems to the deflecting device may not beknown exactly and, further, may vary with time as the tower may rotate.Such deflecting must not damage the rope by excessive static or cyclicstraining or by wearing and clearance requirements within the toweritself must be met.

DISCLOSURE OF INVENTION

The foregoing problems are overcome by performing the rope deflection intwo parts: (1) a fixed deflection into a direction that satisfiesclearance requirements within the tower, and (2) a variable deflectionoccuring at the periphery of the tower to complete the required totaldeflection. Such problems are encountered in guiding the ropes of aguyed offshore oil drilling and production tower from their verticalorientation at the clamping and jacking (tensioning) devices atop thetower to seafloor anchor fixtures which encircle the tower at a greatdistance. The direction of the guylines is not known exactly because ofunavoidable tower misalignment at installation and misplacement of theseafloor fixtures. Further tower movement which may occur during stormsmay vary the direction of the guy ropes by several degrees. Finally,congestion within the tower of structure, wells, and appertenancesnecessitates guiding the guy ropes through these structural elementsfrom a first interior deflection to a second deflection at the perimeterof the tower structure.

The devices of the present invention solve this problem in the followingmanner. A first member fixed in position within the tower bends the ropein a first plane to a predetermined degree. A second member, also fixedin position on the periphery of the tower, bends the rope in the firstplane, if necessary, and, also, deflects the rope in a direction out ofthe first plane. The fixed relative positions of the first and secondmembers maintains a position of the rope which avoids any obstacleswithin the tower and the second member completes deflection of the ropebeyond the tower.

The first member is a shoe having a grooved, curved rope-contact surfaceand a sleeve. The second member includes an outer fixed housing and aninner rotatable housing. The inner housing contains the rope and isprovided with a grooved rope-contact surface and other contact surfacesto accommodate for all rope directions and forces expected. Bearingmeans between the housings permit the inner housing to rotate, thus,increasing the size and variety of potential rope deflections. The innersurface of the inner housing may have a triangular pyramidalconfiguration having rounded corners in which one of the corners of thepyramid forms the groove contact surface for the rope.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic, longitudinal view of a guyed tower marinedrilling and production structure;

FIG. 2 is a top view of the marine structure shown in FIG. 1;

FIG. 3 is a schematic, longitudinal view illustrating the device of theinvention in operational position on a guyed tower;

FIG. 4 is a view taken along lines 4--4 of FIG. 3;

FIG. 5 is a view taken along lines 5--5 of FIG. 3;

FIG. 6 is a schematic, longitudinal view illustrating one part of therope guiding device of the invention secured to a peripheral structuralmember of the guyed tower;

FIG. 7 is a diagrammatic top view of the rope guiding device of theinvention in operational position within the guyed tower;

FIG. 8 is a diagrammatic top view illustrating the use of severalradially extending rope guiding devices on the guyed tower;

FIG. 9 is a cross-sectional view of another part of the rope guidingdevice showing a rope extending therethrough;

FIG. 10 is a view taken along lines 10--10 of FIG. 9;

FIGS. 10A and 10B are similar to the view illustrated in FIG. 10 butshowing, respectively, opposing angular deflections of the rope;

FIG. 11 is another cross-sectional view of the other part of the ropeguiding device illustrating, along with FIGS. 12-17, more the designfeatures of that part;

FIG. 12 is a view taken along lines 12--12 of FIG. 11;

FIG. 13 is a view taken along lines 13--13 of FIG. 11;

FIG. 14 is a view taken along lines 14--14 of FIG. 11;

FIG. 15 is a view taken along lines 15--15 of FIG. 11;

FIG. 16 is a view taken along lines 16--16 of FIG. 11;

FIG. 17 is a view taken along lines 17--17 of FIG. 11;

FIG. 18 is a diagramatic illustration of the manner in which the ropeguiding device operates;

FIG. 19 is a partial cross-sectional view of the other part of the ropeguiding device illustrating one manner of initially pinning the fixedhousing to the rotatable housing of that part;

FIG. 20 is a view taken along lines 20--20 of FIG. 19; and

FIG. 21 is a view similar to that shown in FIG. 20 illustrating analternative means for pinning the fixed and rotatable housings of theother part together.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 illustrate an offshore drilling and producing platform 10supported on a guyed tower 11 founded in the ocean floor 12 by piles (ora spud can or other type of foundation) indicated at 13. A series ofguylines or ropes 14 radiate outwardly from tower 11. Each rope 14 issecured to the upper part of tower 11 at one end and to a suitable clumpweight 15 and pile anchor or heavy drag anchor 16 on the ocean floor atthe other end. A more detailed description of the operation andfunctioning of marine structures of this type may be found in U.S. Pat.No. 3,903,705 entitled "Apparatus for Anchoring Marine Structures" by R.W. Beck et al.

Tower 11 is constructed of a network of tubular structural members, asindicated. Also, production pipes extend upwardly through the interiorof the tower and, in addition, many other appertenances for support ofthose pipes and other required drilling and production equipment arelocated within the confines of the tower.

Referring now to FIG. 3, there is illustrated a rope clamping andjacking (tensioning) device 20 supported on an interior portion ofplatform 10. A deflecting or bending member or shoe 21 is suitablysecured to tower 11, as indicated at 18, vertically below tensioningdevice 20, as shown. As seen in FIG. 4, shoe 21 includes a retainermember 22 containing a grooved, curved rope-contact surface 23 and asurrounding U-shaped sleeve 24. Sleeve 24 holds rope 14 in placepreparatory to tensioning, may contain anti-corrosion and/or lubricatingmaterial, as indicated at 25, and, as noted above, provides forattachment of shoe 21 to the tower.

A deflecting or bending member 26 is fixed in a position located belowshoe 21 on the periphery of tower 11 which is indicated by line 27. Itis secured, as indicated at 28 in FIG. 6, to peripheral support members29 of tower 11. As seen also in FIG. 5, rope 14 extends in a straightline between the aligned lower end of fixed shoe 21 and the upper end offixed member 26. Rope 14 is bent by member 26, as indicated at 30 and31. It is also deflectable out of the plane of the bend of member 21.

The distance L₁ between platform 10 and the uppper end of shoe 21, thehorizontal distance L₂ between shoe 21 and member 26, the verticaldistance L₃ between shoe 21 and member 26, the radius of curvature R_(s)of the shoe and the radius of curvature R_(d) of deflecting member 26will vary in accordance with any particular application. Line 32designates the center line of member 26 which is also the center line ofshoe 21.

The significance of the straight line design is apparent in the diagramof FIG. 7 where there are shown a plurality of production well(conductor) pipes 33 extending vertically within tower 11. Rope 14 mustpass between those pipes, and avoid other appertenances within thetower. The relationship of rope 14 with respect to the interior clampingand jacking device 20, shoe 21 and member 26 are shown in this Figure.

FIG. 8 illustrates a complete arrangement of the several radiallyextending ropes 14, clamping and jacking devices 20, shoes 21 andmembers 26.

Deflecting member 26 is illustrated in more detail in FIGS. 9, 10, 10Aand 10B. It includes an outer (cone) housing 45, and inner (cone)housing 46, and bearings 47 between those housings. Outer housing 45attaches to the supporting structure as illustrated in FIG. 6. Innerhousing 46 contains rope 14, which is shown positioned in a groove 48,and furnishes contact surfaces suitable for all rope directions andforces expected. Bearings 47 transfer forces between housings 45 and 46while permitting inner housing 46 to rotate, thereby increasing the sizeand variety of potential rope deflections. As long as inner housing 46is free to rotate within outer housing 45, any attempt by rope 14 toleave the plane of groove 48 will produce a correcting rotation,indicated by angle gamma (γ), about the axis of housing 46, asillustrated in FIGS. 10A and 10B.

The moment arm is indicated by the arrowed line 55 in FIG. 10. Arrowedline 56 indicates a force which causes rotation of housing 46 to theright as shown in FIG. 10A. The configuration of the interior surfacesof housing 46 is also illustrated in FIGS. 11 through 17. The straightside surfaces 52 and 54 and curved surface 53 and rounded corners 48, 56and 57 form a three-sided pyramidal configuration. While FIG. 17 showsthe smallest end of the opening through housing 46 as being circular inshape it may be shaped as the opening is shown in FIG. 16 or FIG. 15.That end, in any event, is preferably larger than the size of rope 14 asshown in FIGS. 9 and 10.

Lines 60 and 61 illustrate lines of departure of a taut rope 14 fromgroove surface 48 resulting from two different tensions applied to rope14. Line 63 indicates rope 14 in slack position.

Seal rings 70 may be provided between the housings at each end thereofto seal in the bearings. The exterior surface of housing 46 and theinterior surface of housing 45 may themselves comprise bearing surfaceswhich would make separate bearings unnecessary.

The ability of the two-part rope guiding device to deflect the rope 14is illustrated in FIG. 18. Arrowed line 40 indicates the original ropedirection, arrowed line 41 illustrates the orthogonal direction, andnumeral 42 designates the vertical plane of the shoe 21. The anglesalpha (α), beta (β) and gamma (γ) refer to the bend of shoe 21, the bendof housing 46 in the plane of the shoe and rotation of housing 46 aboutits axis, respectively.

Referring now to FIGS. 19 and 20, it may be desirable to releasably pinouter housing 45 to inner housing 46 so that groove 48 of the innerhousing will be in proper alignment with the axis of shoe 21. For thatpurpose, a bolt 71 threadable into housing 46 may be used to pin the twotogether. A diver could release bolt 71 when the device is to be putinto operation. Alternatively, a remotely operated pinning device, suchas the piston-cylinder arrangement 72 controllable by a hydraulic line73, may be used instead. Alternatively, a shear pin could be used.

One manner of installing the device is to install shoes 21 and housingmembers 26 on the tower structure. The ends of ropes 14 are attached tothe anchoring system 15, 16. Each rope 28 is then threaded through thehousing member 26 and shoe 21 associated with it and connected at itsupper end to cable grips connected into the tensioning device 20 onplatform 10. If pinning means to pin outer housings 45 to inner housings46 are used, the two housings are unpinned and ropes 14 made taut undercatenary tension by tensioning devices 20. As the tension forces areapplied when pulling in the ropes the moment arm will cause each innerhousing 46 to rotate to compensate for any directional misalignment ofthe guyed members 21 and 26 with the anchor position. The inner housingmay be rotated manually to any desired position before, during or afterinitially tensioning the rope.

Examples of some equipment sizes, angles and other dimensions which maybe involved in an application of the rope guiding device describedherein to guyed tower follows:

    ______________________________________                                        Rope 14 - 5 inches                                                            Length of Member 26 - 5 feet                                                  Length of Shoe 21 - 15 feet                                                   48 degreesha.     Platform size - 100 feet square                                               Platform height - 1000 feet                                 15 degreesa.      Distance from tower to clump                                                  weight - 2000 feet                                          Distance L.sub.1 - 35 feet                                                                      Distance from clump weight to                                                 pile anchor - 1000 feet                                     Distance L.sub.2 - 85 feet                                                                      R.sub.s - 12 feet                                           Distance L.sub.3 - 50 feet                                                                      Radius.sub.s1 - 6 feet                                      Angle sides 52 and 54 from verticle - 15 degrees                              ______________________________________                                    

The geometry of the surface opposite groove 48 will depend upon theparticular application of the device. The configuration is chosen tosupport slack rope 14 preparatory to tensioning without damaging therope. Consequently, while the preferred embodiment is illustrated withrespect to guyed offshore drilling and production towers the principalof the invention is useful in other applications, marine or land.Although members 45 and 46 are shown conically shaped they may be formedcylindrically, rectangularly or in other shapes. The axis of rotation ofhousing 46 need not necessarily be through the center of the line ofrope 14 extended between members 21 and 26. While the device is shownand described as a two-piece rope guiding device, in some applicationsonly one piece, the bending or deflecting member 26, may be used tocompensate for any misalignment between two members connected togetherby a rope.

Other changes and modifications may be made in the specific illustrativeembodiments of the invention shown and/or described herein withoutdeparting from the scope of the invention as defined in the appendedclaims.

Having fully described the device, objects, advantages and operation ofour invention, we claim:
 1. Rope guiding apparatus for use in anchoringan offshore structure in which a rope extends from said structure to ananchoring system on the ocean floor comprising:a rope guide memberaffixed to said structure and having inner and outer housings; the innersurface of said inner housing forming a three-sided pyramidalconfiguration, one of the corners of the pyramid forming a curvedrope-contacting groove extending in a first plane, said groove and saidrope having substantially the same circumferential radius; said innerhousing being rotatable within said outer housing to rotate and changesaid first plane of said groove to a second plane of said groove to bendsaid rope from said first plane to said second plane to accommodate theposition of the anchor system relative to said platform, the secondplane being the plane of the portion of said rope extending between saidrope guide member and said anchor system.
 2. Rope guide apparatus asrecited in claim 1 including rope tensioning means arranged on saidplatform connected to said rope; and another rope guide member affixedto said platform vertically below said rope tensioning means and capableof bending said rope to extend said rope in said first plane betweensaid rope guiding members.
 3. Rope guide apparatus as recited in claim 2in which said other rope guiding member comprises a shoe having agrooved, curved rope-contacting surface and a curved sleeve surroundingsaid rope-contacting surface.
 4. Rope guide apparatus as recited inclaim 3 in which said one rope guiding member is fixed to the peripheryof said offshore structure below said other rope guiding member, andsaid curved groove being formed in the upper corner of said pyramid andcapable of bending said rope upwardly from said first to said secondplane of said groove.
 5. Rope guide apparatus as recited in claim 4 inwhich said rope guiding members are conically shaped and includingbearings arranged between said inner and outer housings to permit saidinner housing to rotate within said outer housing.
 6. Rope guideapparatus as recited in claim 5 including means for releasably securingsaid inner and outer housings together to prevent rotation of said innerhousing.